In a previous study we demonstrated that repeated maternal separation impaired spatial memory performance in both male and female adolescent rats. The mechanisms of these cognitive alterations are unknown. In the present study, we examined the effects of repeated maternal separation on oxidative stress in the hippocampus, prefrontal cortex and striatum regions of the brain of the adolescent male and female rats. The results showed that repeated maternal separation increased antioxidant enzyme activities and lipid peroxidation in adolescent male rat brains; however, maternal separation did not effects antioxidant enzyme activities and lipid peroxidation in adolescent female rat brains. These results suggest that oxidative stress caused damage in repeated maternal separated adolescent male rat brains, also a strong role of gender in the response of adolescent subjects to maternal separation.